Premature melt solidification during mold filling and its influence on the as-cast structure

Abstract

Premature melt solidification is the solidification of a melt during mold filling. In this study, a numerical model is used to analyze the influence of the pouring process on the premature solidification. The numerical model considers three phases, namely, air, melt, and equiaxed crystals. The crystals are assumed to have originated from the heterogeneous nucleation in the undercooled melt resulting from the first contact of the melt with the cold mold during pouring. The transport of the crystals by the melt flow, in accordance with the so-called “big bang” theory, is considered. The crystals are assumed globular in morphology and capable of growing according to the local constitutional undercooling. These crystals can also be remelted by mixing with the superheated melt. As the modeling results, the evolutionary trends of the number density of the crystals and the volume fraction of the solid crystals in the melt during pouring are presented. The calculated number density of the crystals and the volume fraction of the solid crystals in the melt at the end of pouring are used as the initial conditions for the subsequent solidification simulation of the evolution of the as-cast structure. A five-phase volume-average model for mixed columnar-equiaxed solidification is used for the solidification simulation. An improved agreement between the simulation and experimental results is achieved by considering the effect of premature melt solidification during mold filling. Finally, the influences of pouring parameters, namely, pouring temperature, initial mold temperature, and pouring rate, on the premature melt solidification are discussed.

Key words： premature solidification; mold filling; as-cast structure; modeling

Acknowledgments

This work was financially supported by the FWF Austrian Science Fund (Grant No. P23155-N24), the Austrian Research Promotion Agency (FFG) through the Bridge Early Stage project (Grant No. 842441), the Austrian Federal Ministry of Economy, Family and Youth, and the National Foundation for Research, Technology and Development.

References

1 ‎.  Spittle J,  Dellamore G,  Smith R. Formation of equiaxed zone in small ingots. In: Proceedings of the Conference on the Solidification of Metals. Brighton, 1967, 318–322

2 Stefanescu D M. Science and Engineering of Casting Solidification.New York: Kluwer Academic/Plenum Publishers, 2002, 119–126

3 Winegard W, Chalmers  B. Supercooling and dendritic freezing in alloys.  Transactions of American Society for Metals, 1954, 46: 1214–1223

4 ‎.Chalmers B. The structure of ingots. Journal of the Australian Institute of Metals, 1963, 8: 255–263

5 ‎Jackson K,  Hunt J, Uhlmann  D, On origin of equiaxed zone in castings Transactions of the Metallurgical Society of AIME, 1966, 236: 149–158

6 Southin R T. Nucleation of equiaxed zone in cast metals. Transactions of the Metallurgical Society of AIME, 1967, 239: 220–225

7 Morando R, Biloni  H, Cole G S, The development of macrostructure in ingots of increasing size. Metallurgical and Materials Transactions, 1970, 1(5): 1407–1412

8 Parazian J M, Kattamis  T Z. Effect of reduced gravity on solidification microstructures CH₄Cl-H₂O alloys. Metallurgical Transactions A, 1980, 11(3): 483–493

9 Hunt J D. ‎Steady state columnar and equiaxed growth of dendrites and eutectic. Materials Science and Engineering, 1984, 65(1): 75–83

10 Wu M, Fjeld  A, Ludwig A. Modeling mixed columnar-equiaxed solidification with melt convection and grain sedimentation-Part I: Model description. Computational Materials Science, 2010, 50(1): 32–42

11 Wu M, Nunner  G, Ludwig A, et al. Evaluation of a mixed columnar-equiaxed solidification model with laboratory castings. IOP Conference Series: Materials Science and Engineering, 2012, 27(1): 012018

12 Ahmadein M, Wu  M, Li J, Prediction of the as-cast structure of Al-4.0 wt.% Cu ingots. Metallurgical and Materials Transactions A, 2013, 44(6): 2895–2903

13 Wang T, Wu  M, Ludwig A, Modelling the thermosolutal convection, shrinkage flow and grain movement of globular equiaxed solidification using a three phase model. International Journal of Cast Metals Research, 18(4): 221–228

14 Wang T, Yao  S, Zhang X, Modelling of the thermo-solutal convection, shrinkage flow and grain movement during globular equiaxed solidification in a multi-phase system I. Three-phase flow model. Acta Metallurgica Sinica, 2006, 42(6): 584–590 (in Chinese)

15 Wang C Y, Ahuja  S, Beckermann C, Multiparticle interfacial drag in equiaxed solidification. Metallurgical and Materials Transactions B, 1995, 26(1): 111–119

16 ANSYS, Inc. ANSYS FLUENT 12.0 User’s Guide. 2009

17 Ahmadein M, Pustal  B, Berger R, Grain nucleation parameters for aluminum alloys experimental determination and model evaluation. Metallurgical and Materials Transactions A, 2009, 40(3): 646–653